1. Field of the Invention
The present invention relates to an improved fastening means for safety belts for cars and the like which fastening means is designed especially for resisting the very high G-forces to which the system is subjected in connection with, e.g. a collision. Said safety belt system may, if desired, also be provided with a device reacting very rapidly to a collision and then causing rapid tightening of the safety belt.
2. Description of the Prior Art
Research of late years disclosed that it is of the utmost importance that a person remains sitting as immovably strapped up to the car seat as possible during a car crash if personal injuries are to be avoided in connection with such a crash. This scientifically supported fact is, inter alia, based on the recognition that only a person being completely strapped up to the car seat will be able to benefit fully from the so called deformation zone inherent in the car which is, in turn, crucial to the stopping distance of the car. As known, very high G-forces occur in a collision and the absolute magnitude of said forces will decrease with an increasing stopping distance. With a slack safety belt system, or if the safety belt is stretched the stopping distance will be reduced and the G-forces will, thus, increase.
From the above mentioned it should be obvious that one should aim at having a person/persons follow the deformation cycle of the car to a highest possible extent in a collision, and to achieve this the person/persons must be strapped up so as to become as immovable as possible during the entire collision cycle.
In order to achieve such a result there are, inter alia, developed pyrotechnic devices causing a tightening of the safety belt in the first phase of a collision. This technology involves G-sensitive members (sensors) to be provided and which are calibrated to react at a certain G-value in the front part of the car. When reacting, said sensors generate a signal that is, e.g. via a detonating fuse or electrically, transmitted to a pyrotechnic charge that is ignited and is connected with the shaft of the belt roll which is, in turn, immediately activated to tighten the safety belt. All this occurs during the initial phase of the collision and before any critical G-values are reached. In this manner the person/persons will be kept strapped up to the car seat and will, thus, be in the most advantageous position to face the crash.
As regards the stretchability of the safety belt system, this should, obviously, be as low as possible, ideally the safety belt system should be "dead". When the pyrotechnic charge is ignited G-forces of 2000 to 3000 G will occur at the moment of ignition and these forces are very rapidly transmitted to the safety belt system and, thus, to the fastening means per se. This momentary tightening involving very high G-forces is, thus very critical to the fastening means since the mechanism of the fastening means will "float". Tightening of the safety belt system mainly occurs in the longitudinal direction of the fastening means with a resulting downward pressure on all members of the fastening means. Conventional fastening means are not designed to resist the above mentioned conditions which, inter alia, imply that the fastening means is subjected to exceptionally high G-forces. Consequently, the fastening means will be rendered more or less inoperative, the mechanism, e.g. being unintentionally opened.
Another fact to be mentioned is that developent tends towards more light-weight cars. This will, inter alia result in said stopping or retardation distances becoming shorter than before. This will, in turn, cause greater stress, inter alia, on the fastening means during the catch up phase following after the rapid tightening phase.